Exceptions in dinero make the code unreadable

`args[0]`, `args[0][0][1]` ... this is kind a of unreadable.

It would be nice to have explicit `__init__` on `DineroException` so that we know what's happening.

Like:

``` python
class DineroException:
    def __init__(self, message):
       self.message = message
       super().__init__(message)
```
